As is common, wave power has been utilized for the generation of electrical power for many purposes, including the production of hydrogen and oxygen by electrolysis of sea water. However in the electrolysis of sea water, chlorine is produced which is difficult to handle. For this reason, fresh water or even distilled water is preferred in the generation of pure oxygen and hydrogen.
Systems which use distilled or fresh water require the addition of electrolytes and systems using both solid and liquid electrolytes are common. One system for water electrolysis which utilizes a solid electrolyte is described in an article in the International Journal of Hydrogen Energy, vol. 2, pps. 395-403, Pergamon Press 1977, entitled Conceptual Design of Large Scale Water Electrolysis Plant Using Solid Polymer Electrolyte Technology by L. J. Nuttall.
When shore-based electrolyzers derive power from wave-powered generators, it is important to locate the wave-powered generators close to shore because of the cost of the electrical cable necessary to connect the onshore facility with the generating apparatus, and also because of the rather large losses in the transmission of power over long distances. This presents the problem of sufficient wave activity adjacent the processing plant. As will be appreciated, the terrain adjacent a proposed plant may not provide sufficient wave activity.
Since it is desirable to locate wave-powered generators offshore where sufficient wave activity exists, in order to minimize the distance electrical power is transmitted, it is desirable to have the water electrolysis plant located at the wave power generating site. This requires that the products of the electrolysis, e.g. hydrogen and oxygen, be piped to shore. The losses associated with piping gases over long distances are considerably less than those associated with transmitting electricity. For instance, with respect to oxygen and hydrogen, very little pumping power is required to move the gasses through a pipeline. By way of analogy, in the transportation of natural gas, pressures of 700 psi are sufficient to move the gas over several hundreds of miles without the necessity of providing auxiliary pumping stations. Thus, it is more efficient to provide pipelines for the gaseous products of offshore electrolysis rather than suffering the losses in transmitting electricity over several hundreds of miles to a shore-based facility.
This in turn raises the problem of providing fresh water offshore. As mentioned before, electrolysis of fresh or distilled water results in uncontaminated or pure hydrogen and oxygen. The energy used in pumping fresh water offshore has in the past limited efficient offshore water electrolysis. Aside from the energy expended in the pumping of fresh water to a remote ocean site, there is the problem of expending of energy in any pressurizing or pumping operation associated with water electrolysis. When relying on wave power, the problem of the use of any additional energy for pumping or pressurization becomes actute. Prior art water electrolysis systems require significant amounts of pumping and are thus not well suited for wave-powered offshore operation.
Finally, the manner in which the energy in ocean waves is converted into electrical energy is important. The Lapeyre helix, described below, provides one efficient method of energy conversion. There are however, inefficient wave energy conversion systems involving complicated mechanical structures which are subject to breakdown and are in general not to be left unattended for long periods of time.
By way of further background, a relatively modern system for generating hydrogen by water electrolysis is discussed in the Solar Energy Handbook, edited by Jan F. Kreider and Frank Kreith, published by McGraw-Hill Book Company of New York in 1981, chapter 6, entitled Energy Storage for Solar Applications by Charles J. Swet. This system describes the utilization of deionizers for the feed water to an electrolyzer, a heat exchanger for the O.sub.2 /H.sub.2 O output, and separators for the resulting O.sub.2 /H.sub.2 O and H.sub.2 /H.sub.2 O mixtures.
Another system for producing hydrogen and oxygen by water electrolysis is illustrated by U.S. Pat. No. 3,484,617, in which a wind-driven generator drives a land-based electrolyzer for producing hydrogen and oxygen. In the system described in this patent, pumping energy is necessary in order for the system to operate properly, and offshore capability is not envisioned for this system.
A still further system for conversion of water and development of power is described in U.S. Pat. No. 3,754,147, in which the Bernoulli principle is utilized for the ingestion of air at the air-water interface. In this patent, air is forced into a dome located at the ocean floor. It is the purpose of this dome to pressurize the ingested air, which is then utilized to drive an onshore pneumatic turbine that in turn drives an electric generator. The electric generator is a land-based generator which is utilized to drive a subsurface electrolyzer for the production of oxygen and hydrogen. In this patent, wave motion is utilized to force entrained air to the ocean bottom where it is captured in a dome having its lower periphery exposed at the ocean bed. Note that air pressure drives a land-based electrical generator which supplies an electrolyzer, rather than a wave-driven electric generator directly providing power for the electrolyzer. The interposition of an additional conversion system, i.e. conversion of wave motion to compressed air and then to electrical energy, is inefficient and requires the utilization of an additional pressure dome for the capturing and compression of air.
Finally, attention is drawn to U.S. patent application Ser. No. 147,578, filed by James M. Lapeyre on May 8, 1980 and assigned to the assignee of the present invention. In this application a system is described for manufacturing hydrogen gas which utilizes the energy of surface waves that first converts the energy of surface waves to mechanical energy by apparatus which includes a buoyant helical member mounted for rotation about a horizontal axis, with the pitch of the helical member matched to the length of the expected waves. The helix drives an electrical generator which forms a d.c. current employed to electrolyze ocean water to produce hydrogen gas, which may be compressed or liquified for storage and/or transportation.